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  <title>将数据打包成二进制字符串</title>
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  <div id="layout-content"><div id="function.pack" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">pack</h1>
  <p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">pack</span> &mdash; <span class="dc-title">将数据打包成二进制字符串</span></p>

 </div>
 
 <div class="refsect1 description" id="refsect1-function.pack-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>pack</strong></span>
    ( <span class="methodparam"><span class="type">string</span> <code class="parameter">$format</code></span>
   [, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$args</code></span>
   [, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$...</code></span>
  ]] ) : <span class="type">string</span></div>

  <p class="para rdfs-comment">
   根据<code class="parameter">format</code>将给地的参数打包成二进制字符串。
  </p>
  <p class="para">
   这个函数的思想来自Perl，所有格式化代码（<code class="parameter">format</code>）的工作原理都与Perl相同。 但是，缺少了部分格式代码，比如Perl的“u”。
  </p>
  <p class="para">
   注意，有符号值和无符号值之间的区别只影响函数<span class="function"><a href="unpack.html" class="function">unpack()</a></span>, 在那些使用有符号和无符号格式代码的地方<span class="function"><strong>pack()</strong></span>函数产生相同的结果。
  </p>
 </div>

 
 <div class="refsect1 parameters" id="refsect1-function.pack-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<code class="parameter">format</code></dt>

     <dd>

      <p class="para">
       <code class="parameter">format</code>字符串由格式代码组成，后面跟着一个可选的重复参数。 重复参数可以是一个整数值或者<em>*</em>值来重复到输入数据的末尾。对于a, A, h, H格式化代码，其后的重复参数指定了给定数据将会被使用几个字符串，对于@,其后的数字表示放置剩余数据的绝对定位（之前的数据将会被空字符串填充），对于其他所有内容，重复数量指定消耗多少数据并将其打包到生成的二进制字符串中。
      </p>
      <p class="para">
       目前已实现的格式如下：
       <table class="doctable table">
        <caption><strong><span class="function"><strong>pack()</strong></span> 格式字符</strong></caption>
        
         <thead>
          <tr>
           <th>代码</th>
           <th>描述</th>
          </tr>

         </thead>

         <tbody class="tbody">
          <tr>
           <td>a</td>
           <td>以NUL字节填充字符串</td>
          </tr>

          <tr>
           <td>A</td>
           <td>以SPACE(空格)填充字符串</td></tr>

          <tr>
           <td>h</td>
           <td>十六进制字符串，低位在前</td></tr>

          <tr>
           <td>H</td>
           <td>十六进制字符串，高位在前</td></tr>

          <tr><td>c</td><td>有符号字符</td></tr>

          <tr>
           <td>C</td>
           <td>无符号字符</td></tr>

          <tr>
           <td>s</td>
           <td>有符号短整型(16位，主机字节序)</td>
          </tr>

          <tr>
           <td>S</td>
           <td>无符号短整型(16位，主机字节序)</td>
          </tr>

          <tr>
           <td>n</td>
           <td>无符号短整型(16位，大端字节序)</td>
          </tr>

          <tr>
           <td>v</td>
           <td>无符号短整型(16位，小端字节序)</td>
          </tr>

          <tr>
           <td>i</td>
           <td>有符号整型(机器相关大小字节序)</td>
          </tr>

          <tr>
           <td>I</td>
           <td>无符号整型(机器相关大小字节序)</td>
          </tr>

          <tr>
           <td>l</td>
           <td>有符号长整型(32位，主机字节序)</td>
          </tr>

          <tr>
           <td>L</td>
           <td>无符号长整型(32位，主机字节序)</td>
          </tr>

          <tr>
           <td>N</td>
           <td>无符号长整型(32位，大端字节序)</td>
          </tr>

          <tr>
           <td>V</td>
           <td>无符号长整型(32位，小端字节序)</td>
          </tr>

          <tr>
           <td>q</td>
           <td>有符号长长整型(64位，主机字节序)</td>
          </tr>

          <tr>
           <td>Q</td>
           <td>无符号长长整型(64位，主机字节序)</td>
          </tr>

          <tr>
           <td>J</td>
           <td>无符号长长整型(64位，大端字节序)</td>
          </tr>

          <tr>
           <td>P</td>
           <td>无符号长长整型(64位，小端字节序)</td>
          </tr>

          <tr>
           <td>f</td>
           <td>单精度浮点型(机器相关大小)</td>
          </tr>

          <tr>
           <td>g</td>
           <td>单精度浮点型(机器相关大小，小端字节序)</td>
          </tr>

          <tr>
           <td>G</td>
           <td>单精度浮点型(机器相关大小，大端字节序)</td>
          </tr>

          <tr>
           <td>d</td>
           <td>双精度浮点型(机器相关大小)</td>
          </tr>

          <tr>
           <td>e</td>
           <td>双精度浮点型(机器相关大小，小端字节序)</td>
          </tr>

          <tr>
           <td>E</td>
           <td>双精度浮点型(机器相关大小，大端字节序)</td>
          </tr>

          <tr>
           <td>x</td>
           <td>NUL字节</td>
          </tr>

          <tr>
           <td>X</td>
           <td>回退已字节</td>
          </tr>

          <tr>
           <td>Z</td>
           <td>以NUL字节填充字符串空白(PHP 5.5中新加入的)</td>
          </tr>

          <tr>
           <td>@</td>
           <td>NUL填充到绝对位置</td>
          </tr>

         </tbody>
        
       </table>

      </p>
     </dd>

    
    
     <dt>
<code class="parameter">args</code></dt>

     <dd>

      <p class="para">
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 
 <div class="refsect1 returnvalues" id="refsect1-function.pack-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   返回包含数据的二进制字符串。
  </p>
 </div>

 
 <div class="refsect1 changelog" id="refsect1-function.pack-changelog">
  <h3 class="title">更新日志</h3>
  <p class="para">
   <table class="doctable informaltable">
    
     <thead>
      <tr>
       <th>版本</th>
       <th>说明</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td>7.2.0</td>
       <td>
        <span class="type"><a href="language.types.float.html" class="type float">float</a></span> 和 <span class="type"><a href="language.types.float.html" class="type double">double</a></span> 类型支持打断和小端。
       </td>
      </tr>

      <tr>
       <td>7.0.15,7.1.1</td>
       <td>
        添加了&quot;e&quot;,&quot;E&quot;,&quot;g&quot;和&quot;G&quot;代码以启用float和double的字节顺序支持。
       </td>
      </tr>

      <tr>
       <td>5.6.3</td>
       <td>
        添加了“q”、“q”、“J”和“P”代码以支持处理64位数字。
       </td>
      </tr>

      <tr>
       <td>5.5.0</td>
       <td>
        “Z”代码添加了与“a”等效的功能，以实现Perl兼容性。
       </td>
      </tr>

     </tbody>
    
   </table>

  </p>
 </div>


 <div class="refsect1 examples" id="refsect1-function.pack-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-4543">
    <p><strong>Example #1 <span class="function"><strong>pack()</strong></span> 范例</strong></p>
    <div class="example-contents">
<div class="phpcode"><pre><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$binarydata&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">pack</span><span style="color: #007700">(</span><span style="color: #DD0000">"nvc*"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">0x1234</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">0x5678</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">65</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">66</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</pre></div>
    </div>

    <div class="example-contents"><p>
     The resulting binary string will be 6 bytes long and contain
     the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.
    </p></div>
   </div>
  </p>
 </div>

 
 <div class="refsect1 notes" id="refsect1-function.pack-notes">
  <h3 class="title">注释</h3>
  <div class="caution"><strong class="caution">Caution</strong>
   <p class="para">Note that PHP internally stores <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> values as
    signed values of a machine-dependent size (C type <em>long</em>).   
    Integer literals and operations that yield numbers outside the bounds of the  
    <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type will be stored as <span class="type"><a href="language.types.float.html" class="type float">float</a></span>.
    When packing these floats as integers, they are first cast into the integer   
    type. This may or may not result in the desired byte pattern.
   </p>
   <p class="para">The most relevant case is when packing unsigned numbers that would
    be representable with the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type if it were unsigned.
    In systems where the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type has a 32-bit size, the cast
    usually results in the same byte pattern as if the <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> were
    unsigned (although this relies on implementation-defined unsigned to signed
    conversions, as per the C standard). In systems where the
    <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> type has 64_bit size, the <span class="type"><a href="language.types.float.html" class="type float">float</a></span> most
    likely does not have a mantissa large enough to hold the value without
    loss of precision. If those systems also have a native 64-bit C
    <em>int</em> type (most UNIX-like systems don&#039;t), the only way to  
    use the <em>I</em> pack format in the upper range is to create
    <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span> negative values with the same byte representation
    as the desired unsigned value.
   </p>
  </div>
 </div>

 
 <div class="refsect1 seealso" id="refsect1-function.pack-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="unpack.html" class="function" rel="rdfs-seeAlso">unpack()</a> - Unpack data from binary string</span></li>
   </ul>
  </p>
 </div>

 
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